1. Field of the Invention
The present invention relates to a rotary viscosimeter in which a rotor shaft and a rotor are borne by a pivot and in particular to a rotary viscosimeter having a pivot protection apparatus for protecting the pivot by separating the pivot from the bearing when no viscosity measurement is being taken.
2. Description of the Related Art
There have been developed constant sliding speed type viscosimeters as one kind of rotary viscosimeter. The principle of operation of such a type of viscosimeter for measurement will be described with reference to FIG. 5. As shown in FIG. 5, the rotary viscosimeter of this type comprises a rotary driving shaft 2 of a driving motor (for example, an electric synchronous motor) on which a graduated dial scale plate 3 is mounted, a rotor shaft 5 which is connected with the lower and 2' of the driving shaft 2 via a spring 4 and a rotor 7 secured to the lower and of the rotor shaft 5, which is immersed in a sample liquid 6, the viscosity of which is to be measured. On the other hand, a pointer needle 8 which extends radially above the graduated plate 3 is secured to the rotor shaft 5 so that the angular displacement between the driving shaft 2 and the rotor shaft 5 can be read from the position of the needle 8 on the graduated plate 3.
In the thus formed structure, the viscosity of the sample liquid 6 can be determined from the angular displacement between the rotor shaft 5 and the driving shaft when the torque generated in the rotor 7 due to the viscosity of the sample liquid 6 is balanced with the elastic force of the spring 4. That is, if the spring constant of the spring 4, the size of the rotor 7 and the rotational number are determined, the indication of the pointer needle 8 is proportional to the viscosity of the sample liquid 6. Accordingly, the viscosity of the viscous sample liquid can be determined from the indication of the pointer needle 8.
In the foregoing description of the principle of measurement, the rotor shaft 5, the rotor 7 and the point needle 8 are linked with the lower end 2' of the driving shaft via a spring 4. The section of an actual rotary viscosimeter relying upon which the operation principle relies is shown in FIGS. 6 and 7. FIG. 7 is an enlarged view showing a part A (a pivot and its bearing) of FIG. 6.
The angular displacement of the driving shaft 2 with respect to the rotor shaft 2 can be read as the indication of the needles 8 and 8a on the graduated dial scale plates 3 and 3a as shown in FIGS. 5 and 6, respectively.
The rotor shaft 5a is borne by the pivot 11 and the bearing 12 (actually a gemstone bearing) and is linked with a pointing needle 7 extending upward via the .pi.-shaped linking member 10. The other components such as a driving motor, a graduated dial scale plate 6, a spiral spring 4a, a sample liquid 6a, a rotor 7a and a pointer needle 8a correspond to those represented by the like reference numerals not suffixed with a in FIG. 5. A reference numeral 1' a represents the transmission of a driving motor 1a.
Since the viscosimeter is thus structured, the total weight of the rotor 7a, the rotor shaft 5a, the .pi.-shaped link member 10, the pointer needle shaft and the pointer needle 8a secured to the rotor shaft 5a is imposed upon the contract between the pivot 11 and the bearing 12 as a thrust load. Therefore, a frictional torque is generated on rotation of the rotor shaft 5a. Since the viscosity resisting torque acting upon the rotor 9a may be very low for a specific sample liquid to be measured, pivot friction torque may give an adverse influence upon the measurement of a liquid having a low viscosity, resulting in a lowered measurement accuracy. Accordingly, efforts for reducing the frictional torque have been made by minimizing the radium of the sphere at the tip end of the pivot 11 which is in contact with the bearing 12. Since the load such as the rotor, etc. is supported at one point in such a type of viscosimeter, load conditions at the pivot are very severe in comparison with the other industrial instruments using an ordinary pivot.
The rotor 7a is removed from the rotor shaft 5a or the rotor 7a is replaced with another rotor for washing the rotor 7a after the measurement of the viscosity is completed in such type of viscosimeter. There have been problems that the pivot 11 is deformed by the application of an excessive force to the pivot 11 and damage to the bearing 12 frequently occurs in such a removing or replacing operation. There has also been a problem in that the parts are deteriorated due to vibrations and shocks on transportation of the viscosimeter.
There is also the possibility that the pivot 11 and the bearing 12 are damaged by the application of an external force when removing or mounting the rotor during exchange on normal treatment. Accordingly, operating conditions of the viscosimeter are very severe in comparison with those of the pivot of general industrial instruments. Users of the viscosimeter have to pay careful attention to the operation of the viscosimeter.
A rotary viscosimeter including a protection mechanism for protecting the pivot 11 when the rotor is removed or mounted for exchange or when the viscosimeter is transported has been devised by the present inventors and filed and patented in Japan. (Japanese Utility Model Registration Publication Sho 52-10391).
The pivot protection mechanism of this device is formed as shown in FIG. 8. A cylindrical sleeve 18 which is guided and is axially slidable along the inner wall of the lower casing 17 is provided in the lower casing 17 which houses a pivot 11 and its bearing 12. The sleeve 18 is formed with a thread 18a on the inner wall at the lower portion thereof. A circular disc 19 which is threaded with the internal thread 18a is provided. The disc 19 has in the center thereof a through-hole through which a rotor shaft 5a freely passes. For example, internal gear 20 serving as a lower engaging member is secured to the upper surface of the disc 19. As an upper engaging member which is engaged with the lower engaging member, an external gear 21 having the same pitch as that of the internal gear 30 is provided. The external gear 21 is secured to the rotor shaft 5a. The positions and depths of the gears 20 and 21 are determined so that the gears 20 and 21 are brought into engagement when the sleeve 18 is moved slightly upward from the lowermost position as will be described hereafter.
On the other hand, an opening 17a is provided on the side wall of the lower casing 17. A pin 22 is inserted into the opening 17a. The pin 22 has one end mounted on the sleeve 18 and the other end mounted on a ring-like grip 22 which is vertically slidable along the outer periphery of the lower casing 17. The opening 17a is formed in such a manner that when the pin 22 contacts with the lower end of the opening 17a, an engagement between the internal and external gears 20 and 21 is completely released and when the pin 22 contacts with the upper end of the opening 17a, both gears 20 and 21 are completely engaged with each other and are pushed upward by the disc 19 so that the pivot 11 is completely separated from the bearing 12.
A limit switch 24 comprises a micro-switch and has a pin 24a which is formed as a part of an actuator for the switching operation. The pin 24a is normally projected outwards and is depressed by the upper end of the sleeve 18 when the sleeve 18 is moved upward to a position where the internal and external gears 20 and 21 are brought into engagement. Depression of the pin 24a causes the limit switch 24 to be operated for turning off the power source for a motor 1a for driving the viscosimeter.
When the rotary viscosimeter is not used for measurement, the pivot 11 is separated from the bearing 12 and the rotor shaft 5a is prevented from rotating by positioning the sleeve 18 in an upper position. Accordingly, no damage is caused to the pivot 11 and the bearing 12 even on transportation of the viscosimeter or removing or mounting of the rotor 7a.
Users of the rotary viscosimeter having the above mentioned prior art pivot protection mechanism should conduct operations such as upward sliding of the ring-like grip 23 every time the rotor 7a is exchange after completion of the measurement. Particularly, upward sliding of the ring-like grip 23 for exchanging the rotor 7a is important. There is the possibility that the pivot 11 and/or its bearing 12 may be damaged if there is a failure to carry out the manual sliding operation and the exchange of the rotors is carried out.